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Biological Impacts of a Severn Barrage Les Batty
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Outline A. How important is the Severn? B. The features of an estuary C. What would change with a barrage? D. What would be the biological effects? E. Would it matter? A. How important is the Severn? B. The features of an estuary C. What would change with a barrage? D. What would be the biological effects? E. Would it matter?
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A. How Important is the Severn Estuary? One of largest intertidal zones in UK Ranks 15th in the UK for birds Covered by a suite of international nature conservation designations
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Designated conservation areas Map 14: Designated Conservation Areas
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Wetland of International Importance (Ramsar Convention) Important run of migratory fish - salmon, sea trout, lampreys, allis shad, eel One of most diverse fish communities in UK Internationally important for birds Important run of migratory fish - salmon, sea trout, lampreys, allis shad, eel One of most diverse fish communities in UK Internationally important for birds
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Special Protection Area (EU Birds Directive) Internationally important population Annex 1 species - Bewick’s swan And other species: White-fronted Goose, Shelduck, Gadwall, Pintail, Dunlin, Redshank Internationally important assemblage (>70,000) Internationally important population Annex 1 species - Bewick’s swan And other species: White-fronted Goose, Shelduck, Gadwall, Pintail, Dunlin, Redshank Internationally important assemblage (>70,000)
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Special Area of Conservation (EU Habitats & Species Directive) Estuary, Saltmarshes, Intertidal flats; Sabellaria alveolata reefs; Shads and lampreys. Estuary, Saltmarshes, Intertidal flats; Sabellaria alveolata reefs; Shads and lampreys.
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B. The features of an estuary Physical features
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Mudflats and their ecology Most productive habitat in estuary High water content, even at low tide Organic matter from detritus, phytoplankton, benthic algae, saltmarshes Most productive habitat in estuary High water content, even at low tide Organic matter from detritus, phytoplankton, benthic algae, saltmarshes
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Mudflat fauna
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Mudflat food web
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Saltmarshes Stabilize margins of estuary Important source of primary production Invertebrate fauna Habitat for fish and birds
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C. What would change? Tides Tidal range & velocities reduced by 50% Low water at present mid tide level High water level reduced by c.1m Possible increase in high water stand. Tidal range & velocities reduced by 50% Low water at present mid tide level High water level reduced by c.1m Possible increase in high water stand.
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Processes Longer period of wave action at HW Reduced turbidity/ more light Change in erosion/ accretion patterns Redistribution of sediments Longer period of wave action at HW Reduced turbidity/ more light Change in erosion/ accretion patterns Redistribution of sediments
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Zones Saltmarsh - erosion in some places, expansion in others Intertidal zones - decrease Subtidal - more soft sediment Saltmarsh - erosion in some places, expansion in others Intertidal zones - decrease Subtidal - more soft sediment
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So... The estuary would be altered... But it would still be estuarine The estuary would be altered... But it would still be estuarine
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D. What would be the biological effects? Changes in flora More phytoplankton (more light) More eelgrass (Zostera) More deep water seaweeds More phytoplankton (more light) More eelgrass (Zostera) More deep water seaweeds
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Changes in fauna More zooplankton and suspension feeders, eg.mussels, oysters, scallops Changes in fish community More fish-eating birds (clearer water) Potentially fewer shorebirds More zooplankton and suspension feeders, eg.mussels, oysters, scallops Changes in fish community More fish-eating birds (clearer water) Potentially fewer shorebirds
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So... There would be an impact on the designated conservation areas The biological communities would change, but biodiversity may increase There would be an impact on the designated conservation areas The biological communities would change, but biodiversity may increase
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E. Does it matter? If a significant effect on a Natura 2000 site (SPA/SAC) is likely And the proposal goes ahead for “imperative reasons of over-riding public interest” If a significant effect on a Natura 2000 site (SPA/SAC) is likely And the proposal goes ahead for “imperative reasons of over-riding public interest”
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According to legislation... Measures must be secured to “maintain the coherence of the Natura 2000 interest” (i.e. compensatory habitat provided) According to legislation... Measures must be secured to “maintain the coherence of the Natura 2000 interest” (i.e. compensatory habitat provided)
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But what do you think? How could you find compensatory habitat for the Severn estuary?! and... From an ethical standpoint... Does it matter if the Severn estuary and its ecology changes as the result of a barrage? How could you find compensatory habitat for the Severn estuary?! and... From an ethical standpoint... Does it matter if the Severn estuary and its ecology changes as the result of a barrage?
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